They will occur only through the influx of energy from some source. Aquarium suppliers are perfectly justified in selling air pumps; they are not exploiting the innocent fish-fanciers. Oxidizing a pound of sugar with nitric acid will yield more energy than oxidizing the same pound with oxygen if this seems improbable at first glance, remember the bond energy of the N2 molecule which is one of the products of the first reaction.
Sexual Behaviors | Adolescent and School Health | CDC
Then there is fire, which may be considered as eating its fuel, breaking it down to simpler substances, converting it into its own flaming structure, and eliminating the ash which it can't use.